The research proposed will yield important insights into the mechanisms of inflammatory lung injury . An early step in inflammatory lung injury is the oxidant-mediated injury of pulmonary endothelium. Dr. Gannon has found that endothelial cells undergoing a proliferative response become susceptible to oxidant-mediated injury by neutrophils, and that neutrophils cause an increase in the oxidant-producing enzyme xanthine oxidase in endothelial cells. He now proposes to use rat pulmonary artery endothelial cells, smooth muscle cells, and fibroblasts in cell culture, and isolated vessels in organ culture, to study the interactions between cells in the pulmonary vascular wall. The effects of neighboring cells on growth, proliferation, and oxidant production in the pulmonary endothelium will be studied. Intracellular oxidant production will be evaluated by measuring 1) intracellular activity of the oxidant-producing enzyme xanthine oxidase, and 2) intracellular levels of substrate for the xanthine oxidase enzyme. Changes in xanthine oxidase enzyme activity and substrate availability will be compared to changes in activities and message levels of antioxidant enzymes. These studies will provide important information on cell-cell interactions in the vascular wall, and on the basic mechanisms of oxidant injury in mammalian cells. They may also suggest strategies to control intracellular oxidant production and limit or prevent inflammatory lung injury.